GB2075086A

GB2075086A - Duct linings

Info

Publication number: GB2075086A
Application number: GB8013842A
Authority: GB
Original assignee: FERRANTI RESIN Ltd
Current assignee: FERRANTI RESIN Ltd
Priority date: 1980-04-26
Filing date: 1980-04-26
Publication date: 1981-11-11
Also published as: GB2075086B

Abstract

A duct lining ring or section comprises a tube (10) of fibre reinforced synthetic resin slit longitudinally (12) so that it can be contracted for transport along the duct. The edges of the longitudinal slit are provided with ribs (13, 14) protruding into the tubular section and extending along the edge between which edges a sealing strip (21) is compressed as the edges are butt jointed by sliding or clipping a bridging member (22) onto the ribs. The bridging member and ribs have cooperating projections (19, 20) and recesses (28, 29) which retain the bridging member. The bridging member is shaped to enclose a cavity (30) between it, the ribs and the joint into which a sealing material such as a viscous non-setting fluid is pumped by way of apertures (31) in the bridging member to form a secondary seal to back-up the sealing strip. The ends of the section are shaped to facilitate spigot and socket coupling to other sections. <IMAGE>

Description

SPECIFICATION Lining for ducts This invention relates to linings for ducts, conduits, and culverts, tunnels and the like (hereinafter all referred to as ducts) and to the method of progressively lining a duct by transporting flexible lining sections along the duct to build up a continuous lining shell and pumping grouting material between the lining shell and the duct wall to provide a strong, rigid, lined duct.

British Patent Specification No. 944,064 describes a lining for sewers, culverts, tunnels and like ducts in which a shell is formed in the duct from arch-shaped sections of resin-bonded glass fibre located against an invert of similar resinbonded glass fibre or of concrete. The sections are made relatively thin and flexible for ease of handling and when jointed to other sections, for example by quick-setting resinous bonding agents, within the duct to form a shell spaced by a small distance from the duct wall cement grouting is pumped into the space under pressure.The duct formed has good strength characteristics by virtue of the cement surrounding the shell, good flow and wear-resistance characteristics by virtue of the smooth inner surface and the advantage that sections of more than 1 metre long can be manhandled in the confines of a duct compared with the limitations of handling segments of traditional lining materials such as reinforced concrete without the use of machinery.

The lining described in the aforementioned patent specification adheres to conventional lining practice in retaining a separate arch and invert, even when of the same material, and requires a considerable amount of work to be performed in the duct in making joints between the arch and the invert as well as between sections.

British Patent Specification No. 904,714 discusses the formation of a pipeline by the introduction of a flexible lining (of sheet steel) into an outer lining formed of a steel tube containing spacers or concrete blocks and thereafter pumping concrete grout between the linings to make a large diameter pipe capable of withstanding subaqueous pressures. The lining is introduced into the pipe as a single piece overlapped into a spiral in order to clear the spacers and when in position is expanded and the longitudinal edges joined to form a tube against which the grouting is carried out.

British Patent Specification No. 1 275,268 describes a method of lining a tunnel or conduit with a ring of glass reinforced resin and a surrounding layer of grouting material, as laid down in the aforementioned specification No. 944,064 but introduced as a single piece ring through an already lined portion by the expediency of longitudinally slitting the ring and rolling it into a spiral shape as proposed by specification No. 904,714 for passage to its final location. At its location the ring is expanded to its final shape and the longitudinal slit is sealed to prevent communication between grouting material and the duct (and its contents) by means of a double bonded lap joint carried by one edge of the slit and into which the other edge is located and secured by adhesive.

In such a lining operation, irrespective of the procedure of transporting the lining rings to their final destination the edges of the slit are not easily maintained in juxtaposition by such a simple joining means for sufficient time for an epoxy resin to cure and restore integrity to the ring to withstand grouting pressures. This is particularly so where the lining ring is subjected to external forces such as vibration of the surrounding earth, liquid continuing to flow through the duct and shock due to the placement of other rings.

Furthermore during such curing time particular care is required to avoid contact between the resin and any duct contents which could cause an ineffective seal or reduce the structural integrity of the ring.

It is an object of the present invention to produce a lining ring arrangement and a method of lining a duct which mitigate the above mentioned disadvantages.

According to one aspect of the present invention a duct lining ring, or section, comprises a tube of plastics material slit longitudinally from end to end in order to be contracted in crosssectional area for transport along a duct to be lined, there being provided adjacent each edge of the longitudinal slit for the working length of the tube (as herein defined) an edge region having at least one rib extending into the tube, an elastomeric sealing strip adapted to be sandwiched between the edge regions of the slit, and at least one bridging member adapted to be attached to the ribs of both edge regions and retained by mechanical engagement therewith, to join the edges in a position in which the sealing strip is compressed between the edge regions to seal the joint, the bridging member or members extending for the working length of the tube and being shaped to enclose a longitudinal cavity between the bridging member, the ribs and the sealing strip into which a sealing material can be introduced to provide a secondary seal between the ribs to prevent fluid flow through the joint due to perishing with age of the sealing strip.

In this specification the term 'working length' refers to the part of the tubular section having an inwardly facing wall which is able to come into contact with the contents of the duct and excludes additional end portions adapted to lap part of an adjacent section.

The ribs may be intrinsically moulded with the section during its formation. They may comprise ribs extending along the edge of the slit forming flanges or may be set back from the edge. The ribs may be continuous and extend for the working length of the edge or be discontinuous, effectively being subdivided into a number of shorter ribs.

The ribs may be provided with projections on the sides thereof to engage with corresponding recesses in the bridging member.

The ribs and/or the bridging member may have a resiliently portion deformable to permit the bridging member to engage mechanically with the ribs. The bridging member may comprise two lobes joined to a connecting spine by resilient portions flexible to separate the lobes for attachment to the ribs.

The bridging member may have embedded therein a resilient reinforcing insert of spring steel.

The bridging member may be formed of the same material as the tube. A suitable material for both is a fibre reinforced plastics such as glass fibre reinforced polyester resin or thermoplastic material such as polyvinyl chloride.

The edges of the slit may be aligned to form a buttjoint. The elastomeric strip may then provide a reaction to compression between the edges of the slit to cause each pair of ribs to exert a lateral thrust on the bridging member attached thereto.

The elastomeric sealing strip may be attached to one of the edges between which it is compressed prior to formation of the joint.

The sealing material may be fluid pumped into the cavity after the bridging member is secured.

The fluid may be pumped by way of holes spaced along the bridging member and may be viscous and non-setting or rigidly setting. Where the ribs are set back from the edges so as to be spaced apart in the joint, the cavity between them may be filled with a compressible solid sealing material urged into contact with the slit by the bridging member.

Furthermore, bridging member may be secured to its associated pairs of ribs by means of adhesive if a permanent joint is required.

Each section may have the end regions adapted to form a spigot and/or socket portions for connection with other sections. Each section may have both a spigot portion and socket portion.

Alternatively and preferably each section is of one or two types, a spigot-type in which both end portions are of the same cross-sectional area as the remainder of the tubular section, and form spigot portions, or a socket-type in which both end portions, beyond the working length, are of greater cross-sectional area than the remainder of the tubular section and form socket portions, able to lap and contain the spigot portions, the outer peripheral wall of the spigot portions and inner peripheral walls of the socket portions being provided with co-operating peripherally extending ribs and recesses and an elastomeric strip of sealing material arranged to be trapped by said ribs in said recesses when adjoining sections are coupled.

Each rib may protrude from the surface by an amount greater than the clearance between the peripheral socket and spigot portion walls so that the ribs and recesses may only cooperate by bringing one of the sections to its final size with the spigot and socket portions in their final juxtapositions.

Each spigot and socket section may have at least two ribs or recesses spaced apart longitudinally to define a peripheral cavity between the peripheral walls of a spigot portion located in a socket portion.

Each spigot portion may have at least one aperture in the peripheral wall between the pairs of ribs or recesses by way of which a fluid sealing material may be pumped into said peripheral cavity.

According to another aspect of the present invention a method of lining a duct comprises forming a lining ring or section from a tube of plastics material slit longitudinally from end to end with ribs directed into the interior of the tube and extending along an edge region adjacent the edge of the slit for its working length, contracting the cross-sectional area of the tube by moving the ribs relative to each other, transporting the tube along the duct to align with a tube forming an adjacent section, expanding the cross-sectional area of the tube to locate it in position with respect to said adjacent section and spaced from the peripheral wall of the duct such that the ribs are located at each side of, and spaced apart by, an elastomeric sealing strip, joining the edges by attaching at least one bridging member to the ribs to engage mechanically therewith in a position in which the sealing strip is compressed to seal the slit and to enclose a longitudinal cavity between the bridging member or members, the ribs and the sealing strip extending for the length of the edge region, introducing a sealing material into the longitudinal cavity to fill the cavity and form a seal between the ribs in addition to the flexible sealing strip, and pumping grouting material between the section and the duct wall.

The ribs and bridging member or members may be provided with cooperating projections and recesses and the bridging member may be attached by sliding it along the ribs or by clipping over the ends of the ribs so that the projections engage with the recesses.

The sealing material may be introduced into the cavity as a fluid by at least one aperture in the bridging member. The fluid may be viscous and non-setting such as or a butyl rubber sealant rigidly setting material such as a polyester or epoxide, which also serves to bond the bridging member to the ribs.

The elastomeric sealing strip may be attached to one edge of the slit for the whole length of the tubular section and may be attached before or after transport of the section into the duct.

The tubular sections may be assembled in pairs alternate tube sections having both end regions, beyond the working length, of greater crosssectional area than the closed tube forming sockets to lap spigots formed by end portions of adjacent sections, the outer walls of the spigot portions and inner walls of socket portions being provided with cooperating peripherally extending ribs and recesses, locating the sections such that each spigot portion is located in a socket portion of an adjacent section, expanding the sections to their final size such that each of said peripheral ribs and recesses cooperate with each other to compress a flexible sealing strip therebetween and define a peripheral cavity between each pair of ribs and the spigot and socket walls, and after attaching the bridging member or members to the flanges of the section, introducing a fluid sealing material to the peripheral cavity.

The fluid sealing material may be the same as used in the longitudinal cavity formed by the bridging member or members. The sealing material may be introduced to the peripheral cavity by may be one or more apertures in the spigot walls bounding the cavity.

The bridging member or members may be arranged to correspond in overall length to the ribs in the sections in which employed. Then, the sections comprising the lining may be located in the duct with the joints of adjacent sections offset peripherally.

Whether the joints are offset peripherally or not, the sections are located preferably with the longitudinal joints in the upper part of the duct to avoid wetting of the joints, as far as possible, by contents of the duct flowing through the lining during its assembly.

An embodiment of the present invention will now be described by way of example, with reference to the accompanying drawings, in which:~ Figure 1 is a cross-sectional elevation through a tubular lining section shown contracted for transport through a duct.

Figure 2 is a cross-sectional elevation through a brick walled duct lined with the tubular lining section of Figure 1, Figure 3 is a perspective view of a portion of the tubular section showing how the component parts of a longitudinal butt-joint are arranged, Figure 4 is a cross-sectional elevation through the assembled longitudinal butt-joint, Figure 5 is a section elevation through a plurality of lining sections coupled to form a continuous lining, Figure 6 is a sectional elevation showing in greater detail the encircled portion in Figure 5, Figure 7(a) is a cross-sectional elevation similar to Figure 4 showing a variation in rib positioning, and Figure 7(b) is a cross-sectional elevation similar to Figure 4 showing the joint offset and the bridging member flush with the internal wall of the section, and Figure 8 is a cross-sectional elevation through an alternative form of longitudinal butt-joint.

Referring to Figure 1, a duct lining section is formed from a sheet of glass fibre reinforced polyester resin moulded or rolled to form an incomplete circular tube 10. The tubular section has a smooth internal surface and carries optional lands 11 on an external surface which serve to locate the tubular section substantially centrally within a duct. The edges 12(a) and 12(b) of the sheet, effectively form the boundaries of a longitudinal slit 12 in the wall of a tube.

A pair of ribs 13 and 14 are intrinsically moulded as part of the tube wall and protrude from the inward facing surface edge regions, adjacent each edge and extend for the length of the slit. The ribs are formed at the edges and effectively form flanges which will be described in greater detail hereinafter.

To transport the section to its destination in the duct the flanged edges are overlapped and moved relative to each other to contract the tube in the form of a spiral against the natural memory of the reinforced resin. The tubular section is maintained in a contracted state by means of encircling bands (not shown). When located correctly the bands are released and the tube expanded to its natural size with the ribs 13 and 14 adjacent each other and the slit edges are butt-jointed to form a tube.

Referring now to Figure 2 a sewer duct extending through ground 16 is lined with a ring of bricks. Over a period of time bricks disintegrate or become dislodged and leakage from the sewer is possible. Such leakage, if unchecked, can lead to erosion of the ground in the vicinity of the sewer and subsequent collapse of the sewer and the ground above it.

The lining section 10 is located in the sewer in alignment with other sections and resting on the lands 11 which maintain separation between the tube and the existing brick lining. The section is arranged with the longitudinal slit 12 in the upper part of the duct so that sewer contents and continue to flow by way of the section during installation.

The space surrounding the tubular lining section is filled with a grouting cement under pressure in known manner which sets between the outer original lining 17 and the new inner lining 10 to form a strong rigid structure able to resist [ arge external pressures acting on the relatively flexible lining 10.

The adequacy of the lined duct depends largely upon the ability of tubular section to withstand radial pressures during grouting, the prevention of liquid grouting cement from entering the duct and the prevention of duct contents from contaminating and possibly damaging the grouting cement before and after it has set.

Because of the essentially unitary structure of the lining section and the material from which it is made all the above factors depend on the efficacy of the joint 18 shown as a butt-joint along the edges of the sheet and joints between adjacent sections.

Referring now to Figures 3 and 4, the means and manner of effecting the butt-joint 18 will be described in greater detail.

The ribs 13 and 14 protrude substantially normally to the tube wall, that is substantially parallel to each other. The rib 13 has a rounded projection 19 extending along its edge and directed away from the rib 14 which has a similar rounded projection 20 extending along its edge and directed away from the rib 13. The edge of the slit 12(b) and part of rib 14 has a sealing strip of elastomeric sealing material 21, such as neoprene rubber, attached thereto such that when the tube is restored to its circular shape with the ribs in alignment the sealing strip 21 is sandwiched between them. The sealing strip is narrower than the ribs so that a gap exists between the ribs over part of their width.

An elongate bridging member 22 is formed of a similar fibre reinforced polyester resin and consists of two lobed portions 23 and 24 joined by a spine portion 25. The faces 26 and 27 of the lobes are shaped to conform with the inner wall of the tube section 10 and the lobes are undercut adjacent the spine 25 to form recesses 28, 29. The neck portion between the lobes is slightly smaller than the total thickness of the ribs 13, 14 and the sealing strip 21. The bridging member is attached to the ribs either by sliding it along the ribs with the projections contained in the recesses or clipped onto the ribs by flexing the undercut regions so that the lobes pass over the projections 19, 20 which locate in recesses 28, 29 as the bridging member is pressed into place with the lobes abutting the wall of the tube.

The lobes of the bridging member are forced apart to engage the ribs and the resilience of the bridging member 25 causes a pressure to be applied to the ribs to draw them together slightly to compress the sealing strip 21 which prevents passage of liquid through the slit 12. The resilient reaction of the sealing strip ensures that the bridging member is tightly located against the sides of the ribs.

When the bridging member is located as shown in Figure 4 a non-setting viscous fluid sealing material, such as butyl rubber sealant is pumped into the cavity 30 by way of a series of apertures 31 spaced along the spine of the bridging member. The fluid sealing material fills the cavity between the ribs and is prevented from escape in significant quantity over the faces of the lobed portions by their conforming fit with the tube wall.

The use of a plurality of apertures 31 ensures that the longitudinal cavity is completely filled without air pockets.

The use of a viscous non-setting sealing material in the cavity ensures that the bridging member can be removed subsequently should inspection or maintenance of the joint be required or for contraction and removal of the section. As an alternative to a non-setting sealant a compressible solid may be placed between the ribs and compressed by the bridging member to fill the cavity and provide the second seal.

If circumstances dictate or it is preferred, a hardenable sealing material, such as an uncured polyester, epoxide or urethane resin, may be pumped into the cavity by way of the bridging member. Such material would increase the strength of the butt-joint and make it permanent, while bonding the bridging member to the ribs.

Whichever material is employed for the sealing material the use of a secondary seal in addition to the sealing strip ensures the continuance of sealing should the sealing strip perish with age.

In the above example the sealing strip provides several functions. It accommodates unevenness between the abutting sheet edges and helps form the cavity; its resilience causes the bridging member to be held in place more securely; it prevents the escape of fluid sealing material from the cavity by way of the joint while being introduced under pressure and it prevents the external grouting material from entering the joint.

In lining a duct a number of sections have to be coupled to each other and sealed to prevent leakage. The longitudinal sealing is common to all sections but the sections differ to facilitate such coupling to other sections.

Referring to the plan view of Figure 5 the lining sections fall into two types which are used alternately along the duct. One type, 32, has at both end regions 33 enlarged such that their internal diameters are slightly greater than the outside diameter of the remainder of the section.

Such end regions comprise socket portions for spigot portions formed by the ends 34 of tube type 35. The relationship between the spigot and socket in the coupling between adjacent sections is shown as an enlargement of the encircled portion 36, in Figure 6.

The section through the coupling is shown at the elevation of the longitudinal butt-joint 1 8 so the tubular bodies 10 of socket section 32 and spigot section 35 both have ribs 14 shown thereon, and part of their bridging members 22.

The socket portion 33 is considered additional to the working length of the tube, that is the length of tube which comes into contact with the contents of the duct, and the ribs 14 (and 1 3 not shown) extend only for the working length, terminating at the root of the socket. The slit 12, of course, extends to the end of the section to enable the section to be contracted for transport.

The socket portion 33 contains two recesses 37 and 38 spaced apart and extending parallel to each other around the internal peripheral wall.

Each socket contains a strip 39 of flexible sealing material, such as neoprene rubber, similar to the strip 21 extending along the longitudinal joint.

As mentioned the ribs 13, 14 do not extend into the socket portion but the length of the socket is short compared with the length of the tubular section and the clamping force urged on the ribs by the bridging member serves to clamp the sealing strip 21 between the edge of the slit in the socket portion to form a seal.

The spigot portion 34 is essentially of the same dimensions as the remainder of the tubular section, the ribs 13, 14 extending to the end of the section. The exterior wall of the socket has moulded thereon a pair of peripheral ribs 40,41, spaced apart by the same distance as the recesses 37 and 28. The heights of the peripheral ribs depend on the thickness of the sealing strips 39 but are chosen such that when the ribs are contained in the recesses and the tubular sections are clamped to their final size the ribs compress the sealing strips 39 sufficiently to form a seal to the passage of fluids to and from a peripheral cavity 42 formed between them.

It will be appreciated from the above described coupling that the final diameter of the spigot portion is greater than the internal diameter of the socket. Coupling between two sections is obtained by firstly transporting, expanding and sealing a socket-type section 32.

A spigot-type section is then transported and in contracted state, a spigot end is located in the socket. Then a further socket-type section is transported in a contracted state and located with a socket thereof surrounding the other spigot portion of the spigot section. This further socket section is expanded to final size and the longitudinal joint made with the bridging member.

Then, or simultaneously, the spigot section is expanded such that the peripheral ribs 40, 41 on each spigot end expand into the corresponding recesses in the surrounding sockets. The longitudinal joint is made with the bridging member and a non-setting sealing material pumped into the longitudinal cavity 30 by way of apertures 31.

The peripheral wall of the spigot portion has a plurality of apertures 43 extending into the peripheral cavity 42 which is also filled with the non-setting sealant. A similar aperture 43 extends into a peripheral cavity 42' formed at the base of the socket which is also filled with the sealing material to avoid a trap for material carried in the duct and provide a smooth internal surface to aid flow. Whether the injection of the fluid sealing material and grouting are carried out for each pair of sections or for a larger number of sections is a matter of choice.

The bridging members 22 have been shown as extending for the length of each rib pair with junctions therebetween aligned with the junctions between sections. This, and the pairing of spigot and socket sections, means that any section can be replaced by breaking the longitudinal joint and contracting the section to remove it. In the case of a spigot section only that section is removed, in the case of a socket section that section and adjoining spigot sections require removal, a maximum of three sections. If desired the bridging members 22 could be arranged to bridge the ribs of adjacent sections or the sections could be formed identically, each with one spigot end portion and one socket end portion but the above described removal would be more difficult to implement.

By restricting each bridging member to the ribs of one section only adjacent sections may be located such that the longitudinal joints 18 of different sections are displaced peripherally around the duct. Preferably all of the longitudinal joints 18 are in the upper half of the duct to be clear of duct contents which may continue to flow through the duct as the sections are installed in a re-lining process.

The above described lining and method of installation has related to the relining of an already lined sewer duct but the same techniques may be applied to the inertial lining of an unlined duct, whether a sewer or otherwise.

Also the lining section is not limited to the circular cross-section shown and described above.

For instance sewers are often ovoid or elliptical in cross-section and a tubular section may clearly be formed to conform with the duct. It is equally possible however to employ a lining section of one cross-sectional shape in a duct of another, for example a circular lining section is an elliptical duct, or vice versa, if cost or flow characteristics make this applicable.

In the embodiment described the ribs 13 and 14 are formed as flanges along the edges of the slit. Referring to Figure 7(a) it will be appreciated that the ribs may be set back from the edge. This may enable the formation of ribs having a greater strength that when formed at the edge but also results in an enlarged cavity between the ribs which exists (at least in part) prior to attachment of the bridging member.

With this arrangement a compressible solid or plastic material may be employed as the sealing material and located between the ribs to be compressed and pressed into the cavity and against the slit by attachment of the bridging member.

An alternative arrangement, which is equally suited to the ribs being at the edge or set back from the edges of the slit, is shown in Figure 7(b).

The regions 45, 46 adjacent to the edge of the slit are displaced outwardly of the tube and carry ribs 13 and 14 between which is sealing strip 21. The bridging member 22' is shaped to conform with the wall of the tubular section to cover the displaced edge regions and to form a smooth continuation of the lining section wall.

Other variations in the details described in the above embodiment are possible. Instead of the ribs being moulded intrinsically with the tubular section, that is formed as part of a single moulding, the ribs may be formed separately from the tubular section and by adhesives or mechanically to the edge regions of the section.

Also the bridging member may be formed with reinforcement, particularly where it is intended to attach it by clipping over the ends of the ribs, by embedding a strip of spring steel or other reinforcing material in the bridging member as it is formed. The bridging member instead of being a single structure extending for the length of the edge region may be a plurality of shorter bridging members mounted end to end to form a cavity in the same way.

Furthermore the joint formed along the longitudinal slit need not be a butt-joint described in detail above but may form, for instance, a lapjoint. In such an embodiment (not shown) one of the edge regions may be provided with a plurality of through apertures spaced from the edge and separated therefrom by the rib or ribs of that edge region. The other edge region has a plurality of ribs corresponding to the through apertures and arranged to protrude through them as the edges are lapped, the ribs of each edge portion then extending alongside each other for attachment of the bridging member.

An alternative method of attaching the bridging member to the ribs uses screws, or the like, instead of projections and recesses. Referring to Figure 8 a sectional elevation is shown through a butt joint 50 in which the bridging member 51 is not clipped onto ribs 52, 53 by co-operating ribs and recesses, but in which the bridging member is mechanically secured to the ribs by screws 54 contained in tapped inserts 55. The rib faces 56, 57 distant from each other are tapered and the bridging member is formed with divergent limbs 58, 59 having a co-operating taper with the ribs. As the screws 54 are tightened-the bridging member is moved closer to the ribs and the limbs 56, 57 act as cams on the ribs 52. 53 which are drawn together to compress the seal 50.To facilitate the lateral movement of the ribs relative to the bridging member at least one of the apertures in the bridging member through which the screws 54 pass is elongated. Such an aperture may be employed as an access for sealing material to be pumped into the cavity formed under the bridging member.

All the embodiments detailed above have related to the section and bridging member being formed glass fibre reinforced polyester resin. This material has suitable properties of strength-toweight ratio, enabling lining sections of several metres diameter to be formed and is generally inert chemically. It will be appreciated that any suitable reinforcement and resin composition may be employed to suit the chemical and physical environment in which the lining is used.

The lining and bridging member may be formed of a wide variety of materials, which may be different from each other. The lining section may for instance be formed of a composite or homogeneous thermosetting or thermoplastic material, one example being polyvinyl chloride.

Claims

1. A duct lining ring, or section, comprising a tube of plastics material slit longitudinally from end to end in order to be contracted in crosssectional area for transport along a duct to be lined, there being provided adjacent each edge of the longitudinal slit for the working length of the tube (as herein defined) an edge region having at least one rib extending into the tube, an elastomeric sealing strip adapted to be sandwiched between the edge regions of the slit and at least one bridging member adapted to be attached to the ribs of both edge regions and retained by mechanical engagement therewith to join the edges in a position in which the sealing strip is compressed between the edge regions to seal the joint, the bridging member or members extending for the working length of the tube and being shaped to enclose a longitudinal cavity between the bridging member, the ribs and the sealing strip, into which a sealing material can be introduced to provide a secondary seal between the ribs to prevent fluid flow through the joint due to perishing, with age, of the sealing strip.

2. A lining section as claimed in Claim 1 in which the ribs are intrinsically moulded with the section during its formation.

3. A lining section as claimed in Claim 1 or Claim 2 in which the ribs extend along the edge of the slit.

4. A lining section as claimed in any one of Claims 1 to 3 in which the ribs extend continuously for the working length of the tube.

5. A lining section as claimed in any one of Claims 1 to 4 in which the ribs are provided with projections on the sides thereof to engage with corresponding recesses in each bridging member.

6. A lining section as claimed in Claim 5 in which each bridging member has a resilient portion deformable to permit it to achieve mechanical engagement with the ribs.

7. A lining section as claimed in Claim 6 in which each bridging member has embedded therein a resilient reinforcing insert of spring steel.

8. A lining section as claimed in Claim 6 or Claim 7 in which each bridging member comprises two lobes joined to a connecting spine by resilient portions flexible to separate the lobes for attachment to the ribs.

9. A lining section as claimed in Claim 8 in which the lobes are shaped to conform with the curved peripheral wall of the tubular section and/or the ribs to prevent escape of the sealing material from the longitudinal cavity.

1 0. A lining section as claimed in any one of Claims 1 to 4 in which the faces of the ribs distant from the slit and the co-operating portions of the bridging member are tapered and the ribs carry means for screwing the bridging member to the ribs whereby engagement between the tapered portions forces the ribs towards each other.

11. A lining section as claimed in any one of Claims 1 to S in which a single bridging member extends for the working length of the section.

12. A lining section as claimed in any one of Claims 6 to 11 in which each bridging member is formed of the same material as the lining section.

13. A lining section as claimed in any one of the preceding claims in which the lining section is formed of fibre reinforced plastics material.

14. A lining section as claimed in Claim 13 in which the plastics material is glass fibre reinforced synthetic resin.

15. A lining section as claimed in any one of Claims 1 to 12 in which the plastics material is polyvinyl chloride.

1 6. A lining section as claimed in any one of the preceding claims in which the edges of the slit are arranged to be aligned to form a butt-joint.

17. A lining section as claimed in Claim 16 in which the sealing strip is attached to one of the edges, between which it is to be compressed, prior to formation of the joint.

18. A lining section as claimed in any one of the preceding claims in which the sealing strip is neoprene rubber.

19. A lining section as claimed in any one of the preceding claims in which the sealing material is a viscous non-setting fluid.

20. A lining section as claimed in Claim 19 in which the fluid is butyl rubber sealant.

21. A lining section as claimed in any one of Claims 1 to 18 in which the sealing material is a rigidly setting fluid, operable also to bond the bridging member to the ribs.

22. A lining section as claimed in any one of Claims 19 to 21 in which each bridging member contains apertures for the introduction of sealing material to the longitudinal cavity.

23. A lining section as claimed in any one of the preceding claims including end regions adapted to form spigot and/or socket portions for coupling to other sections.

24. A lining section as claimed in Claim 23 in which each spigot portion comprises an end portion of the section of the same external cross sectional area as the tubular section and socket portion comprises an end portion beyond the working length of the section, of greater crosssectional area than the remainder of the tubular section, able to lap and contain a spigot portion.

25. A lining section as claimed in Claim 23 or 24 in which the outer peripheral wall of a spigot portion and inner peripheral wall of a socket portion are provided with cooperating peripherally extending ribs and recesses, said ribs and/or recesses being provided with an elastomeric sealing strip arranged to be trapped by said ribs in said recesses when adjoining sections are assembled.

26. A lining section as claimed in Claim 25 in which each spigot or socket portion has at least two peripheral ribs or recesses spaced apart longitudinally so as to define a peripheral cavity between the peripheral walls of a socket and of a spigot portion located therein.

27. A lining section as claimed in Claim 26 in which each spigot portion has at least one aperture in the peripheral wall by way of which a liquid sealing material may be pumped into the peripheral cavity.

28. # 28. A lining section as claimed in any one of Claims 25 to 27 in which the ribs are formed on the spigot portion and the peripheral recesses in the socket portion.

29. A lining section as claimed in any one of Claims 25 to 28 in which each peripheral rib protrudes from the surface by an amount greater than the clearance between the peripheral socket and spigot portion walls such that the peripheral ribs and recesses may only cooperate by bringing one of the sections to its final size with the spigot and socket portions in their final juxtapositions.

30. A duct lining section substantially as herein described with reference to, and as shown in, Figures 1 to 6 or Figure 7 of the accompanying drawings.

31. A method of lining a duct comprising forming a lining ring or section from a tube of plastics material slit longitudinally from end to end with ribs directed in to the interior of the tube and extending along an edge region adjacent the edge of the slit for its working length, contracting the cross-sectional area of the tube by moving the ribs relative to each other, transporting the tube along the duct to align with a tube forming an adjacent section, expanding the cross-sectional area of the tube to locate it in position with respect to said adjacent section and spaced from the peripheral wall of the duct such that the ribs are located at each side of, and spaced apart by, an elastomeric sealing strip, joining the edges by attaching at least one bridging member to the ribs to engage mechanically therewith in a position in which the sealing strip is compressed to seal the slit and to enclose a longitudinal cavity between the bridging member or members, the ribs and the sealing strip extending for the length of the edge region, introducing a sealing material into the longitudinal cavity to fill the cavity and form a seal between the ribs in addition to the sealing strip, and pumping grouting material between the section and the duct wall.

32. A method of lining as claimed in Claim 31 in which the ribs and bridging member of members are provided with co-operating projections and recesses and in which the bridging member is attached by sliding it along the ribs.

33. A method of lining as claimed in Claim 31 in which the ribs and bridging member or members are provided with co-operating projections and recesses and in which the bridging member is attached by clipping over the ends of the ribs.

34. A method of lining a duct as claimed in Claim 32 or Claim 33 in which each bridging member is arranged to apply a force to the ribs urging them towards each other.

35. A method of lining as claimed in Claim 31 in which each bridging member is secured to the ribs by forming the ribs and bridging member with co-operating tapered surfaces and screwing (or the like) the bridging member to the ribs such that the drawing of the bridging member to the ribs causes the ribs to be drawn towards each other.

36. A method of lining as claimed in any one of Claims 31 to 35 in which the sealing material is introduced into the longitudinal cavity as a fluid by way of at least one aperture in the bridging member or members.

37. A method of lining as claimed in Claim 36 in which the fluid is viscous and non-setting.

38. A method of lining as claimed in Claim 37 in which the fluid is butyl rubber sealant.

39. A method of lining as claimed in Claim 36 in which the fluid is rigidly setting and also bonds the# bridging member to the ribs.

40. A method of lining as claimed in any one of Claims 31 to 39 in which the elastomeric sealing strip is attached to one edge of the slit for the whole length of the tubular section prior to transport of the section into the duct.

41. A method of lining as claimed in any one of Claims 31 to 40 in which tubular lining sections are assembled in pairs alternate tube sections having both end regions, beyond the working length, forming socket portions to lap spigot portions formed on adjacent sections, the outer walls of the spigot portions and inner walls of the socket portions being provided with cooperating peripherally extending ribs and recesses, locating the sections such that each spigot portion is located in a socket of an adjacent section, expanding the sections to their final size such that said peripheral ribs and recesses cooperate with each other to compress a flexible sealing strip therebetween and define a peripheral cavity between each pair of ribs and the spigot and socket walls, and after attaching the bridging members to the ribs of the sections pumping a fluid sealing material into each peripheral cavity.

42. A method as claimed in Claim 41 when dependent from any one of Claims 36 to 40 in which the fluid sealing material pumped into the peripheral cavity is the same as pumped into the longitudinal cavity.

43. A method as claimed in Claim 41 or Claim 43 in which the fluid is pumped into the peripheral cavity by way of apertures in the walls of the spigot portion.

44. A method as claimed in any one of Claims 31 to 43 in which the bridging member or members extend for the working length of each section in which the lining is formed in the duct with the longitudinal joints of adjacent lining sections offset peripherally.

45. A method of lining a duct substantially as herein described with reference to, and as shown in, the accompanying drawings.